Mark Harris, the Republican candidate, has a slight edge in our poll.

Our poll is a decent result for Republicans. But remember: It’s just one poll, and we talked to only 502 people. Each candidate’s total could easily be five points different if we polled everyone in the district. And having a small sample is only one possible source of error.

This Republican-leaning district stretches from central Charlotte to rural, traditionally Democratic and majority black areas of eastern North Carolina.

This district became a top-tier contest when the Republican incumbent Robert Pittenger was defeated by Mr. Harris in the Republican primary.

Mr. Harris is deeply conservative on cultural and social issues. He’s opposed to gay marriage, questioned whether careers were the “healthiest pursuit” for women and called on women to submit to their husbands in a 2014 sermon.

Mr. McCready is running as a moderate, and emphasizes his military service and religious beliefs. He says he won’t vote for Nancy Pelosi for Speaker of the House.

How our poll result changed

As we reach more people, our poll will become more stable and the margin of sampling error will shrink. The changes in the timeline below reflect that sampling error, not real changes in the race.

One reason we’re doing these surveys live is so you can see the uncertainty for yourself.

If sampling error were the only type of error in a poll, we would expect candidates who trail by four points in a poll of 502 people to win about one out of every six races. But this probably understates the total error by a factor of two.

Our turnout model

There’s a big question on top of the standard margin of error in a poll: Who is going to vote? It’s a particularly challenging question this year, since special elections have shown Democrats voting in large numbers.

To estimate the likely electorate, we combine what people say about how likely they are to vote with information about how often they have voted in the past. In previous races, this approach has been more accurate than simply taking people at their word. But there are many other ways to do it.

Assumptions about who is going to vote may be particularly important in this race.

Our poll under different turnout scenarios

Who will vote?

Est. turnout

Our poll result

Our estimate

208k

Harris +4

People whose voting history suggests they will vote, regardless of what they say

209k

Harris +4

The types of people who voted in 2014

226k

Harris +8

People who say they will vote, adjusted for past levels of truthfulness

227k

Harris +6

People who say they are almost certain to vote, and no one else

260k

McCready +3

The types of people who voted in 2016

315k

Harris +5

Every active registered voter

452k

Harris +2

All estimates based on 502 interviews

The types of people we reached

Even if we got turnout exactly right, the margin of error wouldn’t capture all of the error in a poll. The simplest version assumes we have a perfect random sample of the voting population. We do not.

People who respond to surveys are almost always too old, too white, too educated and too politically engaged to accurately represent everyone.

How successful we were in reaching different kinds of voters

Called

Inter-viewed

Successrate

Ourrespon­ses

Goal

18 to 29

1044

19

1 in 55

4%

6%

30 to 64

10425

320

1 in 33

64%

62%

65 and older

3829

163

1 in 23

32%

31%

Male

6693

228

1 in 29

45%

46%

Female

8608

274

1 in 31

55%

54%

White

10692

342

1 in 31

68%

68%

Nonwhite

4039

139

1 in 29

28%

28%

Cell

11633

337

1 in 35

67%

—

Landline

3668

165

1 in 22

33%

—

Based on administrative records. Some characteristics are missing or incorrect. Many voters are called multiple times.

Pollsters compensate by giving more weight to respondents from under-represented groups.

But weighting works only if you weight by the right categories and you know what the composition of the electorate will be. In 2016, many pollsters didn’t weight by education and overestimated Hillary Clinton’s standing as a result.

Here are other common ways to weight a poll:

Our poll under different weighting schemes

Our poll result

Weight using census data instead of voting records, like most public polls

Harris +4

Don’t weight by education, like many polls in 2016

Harris +4

Our estimate

Harris +4

Don’t weight by party registration, like most public polls

Harris +5

All estimates based on 502 interviews

Just because one candidate leads in all of these different weighting scenarios doesn’t mean much by itself. They don’t represent the full range of possible weighting scenarios, let alone the full range of possible election results.

Undecided voters

About 11 percent of voters said that they were undecided or refused to tell us whom they would vote for.

But if they were to break 2 to 1 in favor of Democrats, that alone would be enough to change the lead in our poll, assuming we did everything else perfectly. (We could also be wrong on turnout or our sample could be unrepresentative. Or other voters could change their minds.)

Issues and other questions

We're asking voters whether they support Brett Kavanaugh's nomination to the Supreme Court and whether they believe the sexual assault accusations against him.

We're also asking voters about feminism and whether they think it's important to elect more women to public office.

Do you approve or disapprove of the job Donald Trump is doing as president?

Approve

Disapp.

Don’t know

Voters n = 502

52%

43%

5%

Would you prefer Republicans to retain control of the House of Representatives or would you prefer Democrats to take control?

Reps. keep House

Dems. take House

Don’t know

Voters n = 502

51%

42%

6%

Do you support or oppose Brett Kavanaugh’s nomination to the United States Supreme Court?

support

oppose

Don’t know

Voters n = 502

51%

41%

9%

As you may know, Supreme Court nominee Brett Kavanaugh has been accused of committing sexual assault when he was a teenager. Would you say you believe the allegations, you do not believe the allegations, or you simply are unable to come to a conclusion?

Believe

Do not believe

Don’t know

Voters n = 502

27%

36%

37%

Do you support electing more people who describe themselves as feminists?

support

oppose

Don’t know

Voters n = 502

41%

38%

21%

Is it important to elect more women to public office?

agree

disagree

Don’t know

Voters n = 502

74%

15%

11%

As you think about your member of Congress, would you prefer your representative to support President Trump and his agenda, or to serve as a check on the president and his agenda?

Support

Check

Don’t know

Voters n = 502

47%

44%

9%

Percentages are weighted to resemble likely voters.

What different types of voters said

Voters nationwide are deeply divided along demographic lines. Our poll suggests divisions too. But don’t overinterpret these tables. Results among subgroups may not be representative or reliable. Be especially careful with groups with fewer than 100 respondents, shown here in stripes.

Gender

Dem.

Rep.

Und.

Female n = 274 / 54% of voters

50%

38%

11%

Male 228 / 47%

33%

57%

10%

Age

Dem.

Rep.

Und.

18 to 29 n = 18 / 5% of voters

40%

56%

3%

30 to 44 77 / 18%

45%

45%

9%

45 to 64 242 / 46%

42%

46%

12%

65 and older 165 / 32%

41%

48%

11%

Race

Dem.

Rep.

Und.

White n = 345 / 68% of voters

33%

59%

8%

Black 79 / 16%

83%

6%

12%

Hispanic 23 / 6%

56%

27%

17%

Asian 6 / 1%

70%

30%

—

Other 26 / 5%

26%

63%

11%

Race and education

Dem.

Rep.

Und.

Nonwhite n = 134 / 28% of voters

66%

22%

12%

White, college grad 208 / 34%

37%

58%

5%

White, not college grad 137 / 33%

29%

60%

11%

Education

Dem.

Rep.

Und.

H.S. Grad. or Less n = 61 / 25% of voters

49%

40%

11%

Some College Educ. 157 / 29%

40%

49%

12%

4-year College Grad. 156 / 28%

36%

55%

9%

Post-grad. 118 / 16%

51%

40%

9%

Party

Dem.

Rep.

Und.

Democrat n = 157 / 32% of voters

87%

6%

8%

Republican 169 / 36%

6%

87%

7%

Independent 158 / 29%

40%

45%

15%

Another party 8 / 1%

45%

51%

4%

Party registration

Dem.

Rep.

Und.

Democratic n = 192 / 39% of voters

75%

13%

12%

Republican 167 / 34%

8%

84%

8%

Other 143 / 27%

38%

48%

14%

Intention of voting

Dem.

Rep.

Und.

Almost certain n = 335 / 69% of voters

44%

46%

10%

Very likely 113 / 23%

39%

53%

9%

Somewhat likely 31 / 5%

35%

39%

27%

Not very likely 11 / 1%

37%

44%

18%

Not at all likely 10 / 1%

39%

28%

33%

Percentages are weighted to resemble likely voters; the number of respondents in each subgroup is unweighted. Undecided voters includes those who refused to answer.

This survey was conducted by The New York Times Upshot and Siena College.

Data collection by Reconnaissance Market Research, M. Davis and Company, the Institute for Policy and Opinion Research at Roanoke College, the Survey Research Center at the University of Waterloo, the University of North Florida and the Siena College Research Institute.